In our case, we use the extra charges, maximum occupancy per site and a requirement that each site reserved must have a camping unit on it as tools to make a large group decide to go elsewhere. Large groups stress our infrastructure. Every additional person in a rig geometrically increases the odds they will need to use the park's showers and restrooms. There is no way 10 people waking up in one rig will be able to use the one toilet and one shower in that rig. Cycling thru everyone would take hours. When that group returns from a day's outing, everyone descends on showers and literally takes them over, leaving all the other guests out in the cold. Same with the laundry and the entertainment items.
We don't want to argue about whether or not we will accept a large family. We don't want to get into questioning whether or not they are all relatives. We don't want to draw lines defining what a family group is or isn't. Great grandma and Grandpa brings their two married kids, who bring their two married kids, who bring their two kids and suddenly allowing parents and children is adding up to 30 people. Instead, we let the fees and policies do the talking. We price large groups at a price that has them saying "no". Takes some of the pressure off us.